The present invention relates to a process for the preparation of an emulsified fuel, i.e. an emulsified mixture of water and at least one organic compound, to be distributed in the same way as other liquid fuels, especially petroleum-based motor fuels and domestic fuel oils. In these fuels, the organic phase is a petroleum product, a vegetable or animal oil or any other fuel used particularly in motor vehicles and domestic boilers and more generally for running internal combustion engines or the like and for running power generating equipment. The invention further relates to a device for the industrial implementation of said process in the form of fixed or transportable industrial units.
The use of emulsified fuel is well known to those skilled in the art, but is difficult to implement because of the lack of stability of the fuel emulsions used. The storage stability of these emulsions has been defined by the Directorate for Hydrocarbons of the French Ministry of Industry. According to this Administration, a water-in-gas oil emulsion is considered to be stable on storage at ambient temperature if no phase separation is observed after at least four months.
Thus patents DE 19 704 874, DD 216 863 and WO 95/33023 particularly describe processes and devices for obtaining fuel emulsions of the diesel type which are installed in terrestrial vehicles. Such fuels are obtained by mixing the components and emulsifying this mixture on the vehicle itself. The emulsions described are ones in which the continuous phase can be aqueous, it being possible for the latter subsequently to be inverted by dilution in an organic phase, as in patent DE 19 704 874. The emulsion described in patent WO 95/33023 contains less than 20% by volume of water, the aqueous phase constituting the continuous phase.
Likewise, patent application WO 92/11927 relates to the preparation of a concentrated emulsion containing from 40 to 80% by volume of water, which consists in separately preparing a fuel oil/emulsifier mixture and a water/alcohol mixture and introducing these two mixtures at two different points into a circulation loop comprising an emulsifying pump, which also serves to circulate all the ingredients in said loop. The concentrated emulsion formed is collected at another point on the loop.
Patent application WO 95/27021 claims an emulsified aqueous fuel of hydrocarbon in water containing 20 to 80% by volume of water, which constitutes the continuous phase of the emulsion, and 2 to 20% by volume of an alcohol, the remainder being formed of hydrocarbons and a non-ionic emulsifier. In said patent application the hydrocarbon is petrol, kerosene, gas oils, synthetic fuel oils or derivatives of vegetable or animal oils. Said patent application also claims a process for the bulk preparation of this emulsified fuel oil, which is stable for at least three months and consists on the one hand of a mixture of hydrocarbon and emulsifier and on the other hand of a mixture of water and alcohol.
None of these patent applications describes a method for the industrial preparation of stable emulsified fuels in which the organic phase constitutes the continuous phase of the emulsion. Now, for obvious reasons of compatibility of the fuel with the parts located between the tank and the system for introduction into the engine, it is preferred to use a fuel whose continuous phase is identical to that of the fuel for which these parts were dimensioned. In the case of emulsified motor fuels whose continuous phase is aqueous, phenomena involving corrosion of metal surfaces and/or premature wear of elastomeric materials can occur. In addition, the combustion of a water-in-oil emulsion is better than that of an oil-in-water emulsion because the sudden vaporization of the water droplets dispersed in the oil considerably improves the dispersion of the hydrocarbons in the combustion chamber (SAE 89 0449 and SAE 92 0464 to M. Tsukuhara et al., SAE 92 0198 to N. Sawa et al.).
The Applicant proposed such a motor fuel in patent application WO 97/34969.
The present invention relates to the preparation of such emulsified fuels whose continuous phase is an organic compound and which can be stable for a sufficiently long period, for example of more than 4 months, to allow their storage in industrial quantities and their subsequent distribution by means of a pump in the same way as motor fuels or other fuels.
The present invention therefore relates to a process for the industrial-scale preparation of an emulsified fuel of water in organic compound(s) whose continuous phase is organic and which contains less than 20% by volume of water and at least one additive necessary for forming the emulsion, said process being characterized in that it consists essentially in:
 1  introducing the additive(s) into a tank equipped with at least one agitator with axial pumping displacement and containing at least the organic compound(s),
 2  homogenizing the resulting volume V of liquid, i.e. organic compounds/additives, with the agitator so that the ratio Qc/V corresponds to:
Qc corresponding to the circulation rate of the liquid inside the tank,
 3  circulating the liquid, homogenized by means of the agitator, in the branch loop emerging in the tank, and through at least one emulsifying system located on said loop, at a rate such that the ratio V/Qcirc corresponds to:
Qcirc corresponding to the flow rate of the liquid in the branch loop,
 4  feeding the aqueous phase necessary for forming the emulsion into the branch loop, upstream of the emulsifying system, and finally
 5  maintaining the homogenization in the tank and the circulation of the liquid in the branch loop until the emulsion has acquired the desired characteristics of storage stability.
This preparative process of the present invention makes it possible to prepare emulsions in industrial volumes, the ratio of water to liquid homogenized in the tank being adjusted during production to give the desired water content in the final fuel emulsion.
To obtain an emulsion of good quality which is stable over time, the steps for preparation of the homogenized liquid, i.e. organic compound(s)/additives, and for emulsification of the liquid with the water are very important, if not essential. Thus it will be possible, during the homogenization and emulsification steps, to heat and cool the liquid contained in the homogenization tank.
According to a preferred mode of carrying out the invention, the process according to the invention comprises a step 1p prior to step 1, during which the additives necessary for the emulsion are mixed with at least one solvent.
The mixture of additives of step 1p is advantageously obtained by diluting the additives in at least one solvent, beginning with the most viscous additive and ending with the least viscous additive, each of these dilutions preferably being carried out in a tank equipped with at least one agitator with axial pumping displacement, for a good homogeneity, and optionally with means for heating and cooling the tank in order to improve the dilution and homogenization of said additives.
During the steps for introduction and homogenization of the additives and the organic compounds in the homogenization tank, it is essential that the additives be dispersed homogeneously throughout the volume of liquid obtained, so that, when water is added, all the additives necessary for forming and maintaining the emulsion are present in sufficient and identical amounts throughout the organic compound. It is not excluded to introduce, into either the organic phase or the aqueous phase of the emulsion formed, additives suitable for improving one or more of the required properties of the fuel according to the invention.
Within the framework of the present invention, the solvent used in step 1p is selected from the group comprising at least one of the organic compounds used to form the emulsion, a solvent of the alcohol, ketone, ester or ether type, and one of the additives of the emulsion which has adequate solvent properties towards the other additives.
The organic compound(s) according to the present invention is (are) selected from petroleum-based fuels, petrols, gas oils, kerosenes and domestic fuel oils, these products optionally being treated with oxygen-containing compounds such as TAME (tert-amyl methyl ether) or MTBE (methyl tert-butyl ether) in the case of petrols, or such as DME (dimethyl ether), DMM (dimethoxymethane) or TEP (triethoxypropane) in the case of gas oils, or refined or unrefined vegetable or animal oils or esterified derivatives thereof.
According to a preferred characteristic of the invention, the emulsifying system will comprise at least one device for circulating the liquid in the branch loop.
The aqueous phase is injected into the homogenized liquid, i.e. organic compound(s)/additives, at a rate Qe proportional to the rate Qc of circulation of the volume V of liquid in said tank, the ratio Qe/Qc varying from 0 to 1.
The ratio Qe/Qc preferably varies from 0.05 to 0.20.
This aqueous phase can also contain specific additives aimed at preventing contamination of the water, such as biocides, or antifreezes, especially in winter, for preventing the water from crystallizing and the emulsion from breaking.
The present process is particularly suitable for the preparation of emulsified fuels of water in oil, especially water-in-gas oil or water-in-petrol emulsions for combustion in internal combustion engines installed in motor vehicles, especially urban vehicles, for which it is particularly desirable to reduce the polluting exhaust emissions by taking direct action on the fuel. Likewise, it can be envisaged to use such a motor fuel for railway or marine applications or in fixed boilers or diesel engines of thermal power stations.
A second subject of the invention is the device for implementing the process, characterized in that it comprises a closed tank (1) equipped with an axial-displacement agitator (2) and comprising three fluid inlet lines (3), (4) and (5), for the organic compound(s), the additives and the emulsion respectively, a fluid outlet line (6) and optionally a heating and/or cooling system, the lines (5) and (6) being connected to a circulation line (7) defining a branch loop, which comprises a water inlet line (9) and an emulsifying system (8), and finally a discharge line (10) for the emulsified fuel. This line (10) could be placed either on the tank (1) or on the branch loop (7), upstream or downstream of the emulsifying system (8).
In the device according to the present invention, the line (4) serves to inject the mixture of additives, which has initially been prepared and homogenized in a second tank (11) equipped with an axial-displacement agitator (12) for homogenizing said mixture of additives, and comprising inlet lines (13) and an outlet line (4) for the mixture, and optionally a system for heating and/or cooling said tank (11). It is possible to use any type of heating and/or cooling insulation appropriate for a tank of industrial dimensions. The lines (3) and (4) could be merged into a single line for introducing the organic compounds and/or the additives into the tank (1).
In the tanks (1) and (11) the agitators (2) and (12) must enable the whole of the liquid contents to be homogenized and must promote the circulation of the liquid in the tank without creating a shear gradient between two points, i.e. by homogenizing at a variable defined shear rate. The chosen agitators (2) and (12) will preferably be axial-displacement agitators, which permit longitudinal agitation relative to the axis of rotation and have a high pumping capacity.
The emulsifying system (8) according to the present invention comprises at least one emulsifying pump and/or one or more dynamic mixers equipped with a rotor/stator with a narrow air gap (fixed or variable) and rotating at high speed, i.e. at more than 2000 rpm.
Downstream or upstream of this emulsifying system, or instead of it, one or more static mixers and/or one or more other emulsifying machines operating by mechanical action or by means of ultrasound and/or microwaves, cooperating in the formation of the emulsion, can be placed on the branch loop (5, 6, 7).
To promote the dispersion of water droplets in the oil, at least one droplet dispersing system, for example a cartridge or a distributor made of sintered metal or stainless steel fiber and containing very fine pores of one to several tens of microns, can be fitted to the water injection line.